Exactly one quarter of all music sold in the US now comes from iTunes, the NPD Group said today. Its portion of the market for the first half of 2009 is up from 21 percent in 2008 and represents 69 percent of the digital-only market. By comparison, Walmart now has just 14 percent of all music while Best Buy claims third place with an unspecified amount. In digital, Amazon MP3 is a distant secon
